She’s in the river. This happened in Worcester a few years ago with a lad called Tom Jones, huge searches, even arrests made then lo and behold a few weeks later his body surfaces a bit further down the river. Hypothesis being he was drunk, probably got a bit too close to the river walking back to his digs and fell in.
The police will have checked every route to and from that area and obviously know things we don’t-I’m sure they would say if they believe she’s been abducted.
Whether she went in herself or someone else is responsible for her going in I don’t know.